But in recent tests, researchers identified some DEET-insensitive Aedes aegypti mosquitoes—a species that carries the diseases dengue and yellow fever—by observing which insects bit DEET-treated human arms. The team then discovered that a gene alteration stopped a sensory cell on the bugs' antennae from detecting the chemical. (Read about DEET-free insect repellents in the Green Guide.)

And when the team bred these mutated females with males of unknown sensitivity, the proportion of DEET-oblivious mosquitoes rose from 13 to 50 percent in one generation, the team reported May 3 in the journal Proceedings of the National Academy of Sciences.

Little Risk of Superbugs

But the risk of a race of invincible superbugs isn't that great, Logan cautioned.

That's because there will still be enough regular mosquitoes to crossbreed with those that can't sense DEET.

"You'd have to have every single person [in the world] using DEET all the time" for the resistant bugs to spread, he added.